Transcranial direct current stimulation (tDCS) is a form of neurostimulation which includes, for example, delivering a constant and low current directly to a brain region of a person, namely a subject, through electrodes; such a low current is optionally in a range of 0.5 mA to 2 mA, but is optionally greater than 2 mA, or less than 0.5 mA in certain circumstances. tDCS is useful, for example, for treating patients with brain injuries, such as strokes, for treating depression, anxiety, tinnitus, chronic pain, and for enhancing language and mathematical abilities, addressing attention span problem, for enhancing problem solving abilities, for improving memory, and for enhancing a coordination of body movements.
A known tDCS device includes an anode, a cathode and a battery powered device that is operable to deliver a constant current signal; optionally, the known tDCS device is also susceptible to being mains-powered from an electrical supply network. The anode is a positively charged electrode and the cathode is a negatively charged electrode. During treatment, one of these electrodes is placed over a head region of a person and another electrode is placed at another location, such as a neck region or shoulder region of the person. Once the electrodes are placed correctly, a stimulation procedure may be started. The battery- and/or mains-powered device includes one or more controls for setting the current signal as well as for adjusting a duration of the stimulation procedure. The constant current signal flows from the anode through a skull and brain of the person and thereafter to the cathode, creating an electrical circuit.
Spatial positions of the anode and the cathode on person's head is crucial, as different medical disorders require modulation of different brain regions, and consequently different spatial positions of the anode and cathode on person's head, and a slight variation in a relative spatial distance between the anode and cathode may significantly influence an effectiveness of such treatment. Conventionally, medical professionals, i.e. doctors, manually place the anode and cathode on the person's head in accordance with an internationally recognized ‘10-20 system’, which is a system for describing locations which are appropriate when applying scalp electrodes in a context of an EEG test or experiment. This system is based on a relationship between a location of a given electrode and a corresponding underlying area of cerebral cortex. The “10-20 system” uses locations of cranial landmarks, such as nasion, inion, left and right tragus to determine electrode positions on the scalp. The “10” and “20” refer to the fact that actual distances between adjacent electrodes are either 10% or 20% of the total front-back, namely nasion to inion, or right-left, namely right tragus to left tragus, distance of the skull of the person.
However, the manual placement of electrodes by doctors is susceptible to positional errors, and even a small positional error may affect the overall effectiveness of the treatment. A correct placement of the electrodes is particularly important when the electrodes are used to deliver therapeutic stimulation in repeated stimulation sessions on, for example, consecutive days. In other words, an accurate reproduction of a stimulation site is therefore important. Therefore, there exists a need for a method and system that monitors positions of electrodes on a given head region, or forces the positions based on anatomical markers, that enables the positional errors of electrodes to be reduced, and facilitates repositioning the electrodes for an improved transcranial stimulation.
In a scientific publication “Transcranial direct current stimulation: State of the art 2008” (Nitsche et al., Brain Stimulation (200) 1, pp 206-223, Elsevier), positions for placement of electrodes for performing transcranial stimulation are provided, for example as shown in FIG. 1 of this publication. Various issues associated with transcranial direct current stimulation (tDCS) are described, including side effects resulting from electrochemical reactions occurring at positions where associated electrodes are placed on a head region of a given person. Effects experienced by the given person when subject to tDCS are described in the scientific publication, for example in comparison to transcranial magnetic brain stimulation.